Unicontrol signaling system



April ls, 1930.. I L. HAZELTINE 1,755,114

' UNICONTRCL SIGNALING SYSTEM Filed April s, 1925. r 2 Sheets-Sheet 1INVENTOR ATTORNEYS April 15, 1930. L. A. HAZELTINE UNICONTROL SIGNALINGSYSTEM Filed April 3, 1925 2 Sheets-Sheet 2 Angular adjmsfmenl(fl/lsp/acemenfj fic,

- [NVENTOR W ATTORNEYS Patented Apr. 15,

UNITED STATES PATENT OFFICE LOUIS A. EAZELTINE, OI HOBO KEN, NEW JERSEY,ASSIGNOR' '10 HAZEL'I'INE B- POBA'IION, OF JERSEY CITY, NEW JERSEY, ACORPORATION 01 DELAWARE UNICON'IBOL SIGNALING SYSTEM Application filedApril 3, 1925. Serial No. 20,484.

This invention relates to radio amplifiers and radio receivers.

The circuit arrangement for reception of radio signals which hasproducedexcellent 5 results because of its sensitivity and selectivity is thatemploying tuned radio-frequency amplification in several stages, withelimination or neutralization of coupling between stages, as describedinmy United States Let- 1 ters Patents No. 1,489,228, No. 1,533,858, No.1,577,421 and N 0. 1,648,808. While receivers of this type have met withalmost universal approval from users, it has been recognized that itwould be highly desirable to reduce the means for tuning to a singlecontrol, and further to obviate the need of an external antenna.

Telephone transmitting stations employ undamped carrier currents, theoscillations of which have no decrement, so that the incoming signalscan be received in closely coupled and sharply tuned circuits. Theemployment of undamped carrier currents permitting the use of closelycoupled and sharply tuned circuits has previously necessitated anindividual control for each of the several stages. This multiplicity ofcontrols is due to the fact that manufacturers have been unable, inpractical construction, to produce coils and condensers withsubstantially no variation in electrical characteristicsa conditionwhich must be met if a single control is to be employed for tuning aplurality of circuits exactly. Where a common control wasformerlyprovided to vary simultaneously the tuning of all the circuitsof a radio receiver, the mentioned manufacturing variations introducedwide inequalities, with resultant detuning in the respective stagesthroughout at least a portion of the intended operating range, oreffective frequency band, because no means ware/provided to adjust allstages ,once and for all to have identical electrical characteristicsover the entire operating range. The inevitable result of this detuningwas a serious impairment both of amplification and selectivity.

There have been proposed so-called master-control radio-frequencyreceivers in which a single control is provided for the purpose ofroughly tuning, simultaneously, each of several clrcuits, a number ofseparate con-. trols being provided to tune the individual circuits toexact resonance, thereby overcoming the mentioned detuning which resultsfrom inequalities in the-elements of -those circults. This system, ofcourse defeats its own purpose, since there are actually at least asmany controls as there are circuits to be tuned.

Furthermore, receivers are frequently used with antennas improperlyerected by those unfamiliar with the preferred characteristics of suchstructures, so that such antennas Vary widely in their constants, andconsequently the tuning of the circuit immediate- 1y associated with theantenna system is affected within wide limits.

One of the main advantages of this invention resides in its applicationto a multistage radio-frequency amplifier wherein a single control maybe employed, as distinguished from the previously discussedmaster-control together with supplemental controls for the individualstages.

Another feature of the invention resides in the provision of a completeantenna system entirely supported by a cabinet.

Referring to the drawings:

Fig. 1 shows a plan view of a radio receiver embodying this invention,with the tain parts broken away to disclose the in-.

terior arrangement of parts;

Fig. 1 shows a side elevational view of this receiver with a side wallremoved;

Fig. 1" shows a form of electrostatic scree utilized in the preferredembodiment of this invention;

Fig. 1 shows the complete circuit diagram of the receiver illustrated inthe figures above;

Fig. 2 shows a calibration curve of a variable condenser; and

Figs. 2 and 2 show two views of a referred constructionfor the variablecon ensers, including the two adjustable features; Fig. 2 being asectional view taken along line 2 of Fig. 2".

Referrin to Figs. 1, 1 and 1, there is shown a ra '0 receiver cabinetwith an upper compartment 5, 6, 7 and 8 within which are mounted coils TT,, T,, a multi-unit condenser with units C1, C, and (3,, vacuum tubes VV,, V,, V an audio-frequency transformer AF, and all necessary batteriesenclosed in a metal container. It will be noted that'the mentionedcoils, in order to minimize undesirable magnetic coupling between them,are mounted in a row at one side of the compartment with their axesinclined at an angle of approximately to their common line of centers.The shaft of the multi-unit condenser is mounted in bearings supportedat the front and rear of the compartment and is arranged to be rotatedby a control or pointer 26 which moves over a scale 27 on the panel orfront of the cabinet. At 25 there are shown rheostats for controllingthe heating current of the vacuum tubes. The interior of the mentionedcompartment may be lined with an electrostatic screen in the form ofzig-zag wires, such as 9, indicated in Fig. 1", and similar wire screens9 indicated by dotted lines in Fig. 1 may be employed to rtially shieldthe stages from each other. Etch section of the screens should referablybe connected at one point to the ow-potential side of the filamentcircuit. This system of screens, together with the batteries and theircontainer appearing in the upper right hand corner of Fig. 1', may, dueto the resulting large conducting surface, serve as a counterpoise inthe antenna system. In this way the conductin surface is made large andthe resistance of t is portion of the antenna system reduced. At thelower portion of the cabinet there is mounted a metal sheet 1, servingas an antenna, which is connected to the first tuning coil T by means ofa metal rod 2. In the space betweenthe metal sheet 1 and the uppercompartment, there may be supported in any convenient manner aloud-speaker mechanism 4 and an amplifying horn 3.

The above-described arran ement of counterpoise and antenna provi es anantenna 111 of very low radio-frequency resistance and of fairly highcapacity relative to the linear dimensions, although the effectiveheight is low. The low resistance and moderate capacity of the antennamake desirable cation and one stage of audio-frequency amplification,provided it is desired to receive well only those stations which arenear enough not to have pronounced fading, orto be affected seriously byatmosphericdisturbances. While, as has been stated, the preferredembodiment includes a self-contained antenna, the value of thisinvention resulting in extreme simplicity of control may be had withantenna and ground exterior to the cabinet, if there be provided in theantenna circuit a condenser of such capacity that small changes incapacity resulting from changes in antennas are negligible as comparedwith the resultant capacity of the condensers; or if such antennacondenser be arranged to be adjusted once for all with the particularantenna employed.

A convenient and compact form of tuning condenser is that havingcircular moving plates. This form of condenser gives within its workingrange a straight line relation between capacity and angular adjustment,-

or displacement, as illustrated in Fig. 2". To carry out the purpose ofthis invention, it is necessary that the condenser plates be rigidly andaccurately plane and parallel, so that the calibration curve, Fig. 2,will be identical in shape for all condensers. This curve shouldpreferably be a straight line. However, there will still exist therobability of differences in the various tuna le oscillatory circuits,due to differences in the fixed capacities of the wiring and of thecoils, etc.; and there may also be variations in the clearances of theplates of the different condensers that will cause their rates of changeof ca acity to differ slightly from one another. 0 compensate for thefirst condition a supplemental or auxiliary adjustable plate 10, shownin Figs. 2 and 2, electrically connected to the moving plates, but notmoving with them, is placed adjacent to one of the outer stationaryplates and is adjusted relatively to that plate, when the receiver isfirst assembled, so as to tune both radio-frequency amplifier inputcircuits and the detector input circuit to the same maximum resonantfrequency when the main variable condenser units are set for minimumcapacity.

While for the purpose of this invention ad justable plate 10 can besupported in any convenient manner, for it may, for example, be mountedas illustrated in Fig. 2". The construction there represented provides athreaded journal 13 surrounding the condenser shaft 12. On the inner endof this journal there is an integral collar 15 against which a nut 14forces the condenser plate 10. Another nut 17 holds the journal tightlyto the insulating plate 16 and serves to lock the assembly after theproper adjustment has been made.

To com ensate for the differences in the rates of c ange of capacity ofthe various condenser units, or in the rates of change of resonantfrequenc of the oscillatory circuits ,in which the con enser units areconnected,

the outside stationary plate 11, Fig. 2", is arranged to be moved axlallThis latter adjustment is made when t e receiver is first assembled soas. to tune all three radiofrequency input circuits to the same minimumresonant frequency when the main vari able condensers are set formaximum capacity. This adjustment may affect slightly the initialadjustment of plate 10 which may now have to be readjusted. The finalresult of these adjustments is that all of the tuned circuits will be inresonance with one another for every setting of the tuning condensers,because the calibration curves are straight lines (or else are exactlysimilar) and, having been made to coincide at two points, coin cidethroughout. In other words, the slopes of the capacity-displacementcurves of the several condenser units will be identical. When all thetuning condenser units are provided with these adjustable features, itis, possible to engrave a wave-length or frequency scale 27 on thepanel, prior to assembly, and to permanently adjust all condenser unitsto suit this scale.

The adjustment 'of plate 11,-Figs. 2 and 2, will also compensate foraccidental differences in the self-inductance of the tuning coils.Mechanical forms of adjustment other than those indicated in Figs. 2 and2 are, of course, possible, but, in general, they should be such as todetermine or vary, first, the fixed or minimum value of the tuningcapacity (or maximum resonant frequency), and second, the rate of changeof capacity (or resonant frequency) with given displacement of thetuning control.

It is possible to use other shapes of condenser plates than that givingthe straightline-capacity calibration curve of Fig. 2, as, for example,condenser plates so shaped that when the condenser is connected across asuitable inductance, they will produce a straightline-frequency curve;but such calibration curves must agree with one another in the respectthat their ordinates when plotted from some particular axis for each arepro- J portional throughout.

The apparatus previously described may be connected in a circuit arranement similar to that shown in Fig. 1. nthis figure there are shown twosta es of tuned radiofrequency amplification including the vacuum tubesV and V a detector tube V and an audio-frequency amplifier including thetube V A greater or less number of stages of radio-frequency or ofaudio-frequency amplification may be used, if desired, without departingfrom the spirit of this inven tion. The first tuned circuit of thisdiagram includes the electrostatic capacity of the antenna system abovereferred to which is not present in the tuned circuit of V, or the cirofV These two capacities will, in part,

balance each other, the difference being taken care of bythe factoryadjustments of the variable condensers, as previously described. Aneutralizing "condenser (J connected between the grid circuit of vacuumtube V and the secondary winding of transformer T tother with a secondneutralizing condenser 5: connected between the grid circuit of vacuumtube V and the secondary winding of transformer T function to eliminateundesirable inherent capacity couplings, and hence to preventregeneration and a corresponding tendency towards oscillations.

The presence of regeneration control is incompatible with the unitarytuning control of aplurality ofsuccessive tuned stages in a vacuum tubeamplifying system because any appreciable variation in the regenerationadj ustments necessitates a corresponding variation in the tuningcontrol of those stages only in which the regeneration occurs. Thedegree of regeneration and the corres onding tendency towardsoscillations is argely determined by naturally variable factors, such asthe condition of batteries, i. e., the internal resistance thereof, thesettings of the filament rheostats and the characteristics of the vacuumtubes, because these and other factors influence the effectiveness ofthe coupling between the output and input circuits of the tube or tubes.It therefore follows that in order to render unnecessary the detuning ofany of the stages for oscillation control and to attain efiicientsimultaneous tuning of the several successive circuits everyreasonableprecaution should be taken to prevent regeneration. To this end anembodiment of the present invention is herein described as includingmeans for neutralizing or eliminating substantially all undesiredcapacity coupling, electromagnetic coupling and other forms of undesiredcoupling, whereby regeneration is substantially prevented. It isunnecessary to describe further the functions of the various circuitssince they are fully disclosed in my mentioned patents. It will beunderstood, however, that the tuning of the circuits of V V and V issimultaneously and uniformly accomplished since the condenser units C1,C and C of these circuits are controlled by the common rotatable shaft12.

I claim:

1. In a wave signaling system, the combination of an inductance coil, avariable condenser connected thereto, said coil and condenser togethercomprising a tuned circuit, and two independent adjusting means for saidcondenser, the adjustment of one of which determines the maximumresonant freuency of said circuit, and the ad ustment of t e other ofwhich determines the rate of change of resonant frequency of saidcircuit.

a wave signalin system includinga tuned multi-stage amp ifier each stage'of which includes an oscillatory circuit comprising a coil and avariable condenser, said condenser having aplurality of adjustingmeans,a plurality of said circuits being simultaneously tunable by a commoncontrol, the method of renderin said circuits in resonnance with eachother throughout their intended operating frequenc range, whichcomprises adjusting one 0 said means to bring said circuits intosubstantial resonance at a certain frequency, and adj ustlng a second ofsaid means to determine the rate of change of resonant frequency whenthe frequency is variedcby said tuning control common to said cicuits.

3. In a wave signaling system including a tuned multi-stage amplifiereach stage of which includes an oscillatory circuit comprising a coiland a variable condenser, said condenser having a plurality of adjustingmeans, a plurality of said circuits being simultaneously tunable by acommon control, the

method of rendering said circuits in tune with each other throughouttheir intended operating frequency range which comprises adjusting oneof said means to bring said circuits into substantial tune at a certainmaximum resonant frequency and adjusting a second of said means to bringsaid circuits into substantial resonance at a certain minimum resonantfrequency, whereby the adjustment of said tuning control simultaneouslyvaries the resonant frequency of said circuits While the same arerendered substantially in tune with each other throughout the intendedoperating frequency range.

4. In a wave signaling system, the combination of an inductance coil, avariable condenser connected thereto, said coil and condenser togethercomprising a tuning circuit, and adjusting means for said condenserwhereby the maximum resonant frequency of said circuit and the rate ofchange of resonancefrequency of said circuit may be substantiallyindependently adjusted.

5. In combination with a radio-frequency signaling system wherein aplurality of tuned oscillatory circuits are simultaneously adjusted by aunitary control, a variable condenser connected in each oscillatorycircuit to tune the same by variation of its electrostatic capacity,said condenser being characterized in that it includes three separateadjusting means, the first of which determines a minimum capacity value,the second of which determines a maximum capacity value, and the thirdof which effects a variation according to a predetermined manner in thevalues of electrostatic capacity between said minimum and maximumcapacity values.

6. In a radio-frequency signaling system wherein a plurality ofoscillatory circuits are simultaneously tunable over a certain frequencyrange by a unitary control, means supplemental to said control foradjusting the rate of charge of resonant frequency of at least" one'ofsaid circuits.

7'. In a wave signaling system wherein a plurality of oscillatorycircuits are simultaneously tunable over a certain frequency range by aunitary frequenc -control, adjusting means connected in eac of saidoscillatory circuits whereby the rate of change of resonant frequency ofeach of said circuits may be individually adjusted.

8. In a wave signaling system wherein a plurality of oscillatorycircuits are simultaneously tunable over a certain frequency range by aunitary frequency-control, a plurality of adjusting means connected ineach of said oscillatory circuits whereby the maximum resonant frequencyof each of said circuits and the rate of chan of resonant frequency ofeach of said circuits may be individually adjusted.

9. In a tuned radio-frequency amplifier having a plurality ofoscillatory circuits simultaneously tunable over a certain frequencyrange by a unitary control, means supplemental to said control forindividually adjusting the rate of change of resonant frequency ofcertain of said circuits whereby said oscillatory circuits may bemaintained substantially 1n resonance with each other when tuned oversaid frequency range by said unitary control.

10. In a wave signaling system, the combination of an inductance coil, atuning condenser having means for varying the capacity thereof, saidcoil and condenser being connected together to comprisean oscillatorycircuit, and frequency-adjusting means for said circuit whereby themaximum resonant frequency of said circuit and the rate of change ofresonant frequency of said circuit may be adjusted supplementally ofsaid means for varying the capacity of said condenser.

11. In a radio-frequency signaling system wherein a plurality ofoscillatory circuits are intended to be simultaneously tunable over thesame frequency range by a unitary frequency-control," means supplementalto said control for adjusting the slope of the frequenc -displacementcharacteristic of said unitary requency-control for certain of said.cies as there are means ity of substantially independent meansassociated with a certain one of said circuits and supplemental to saidcontrol to adjust said certain circuit at as many differentfrequenrovided so that more than one of said circuits are resonant witheach other thruout said frequency range.

13. In a wave signaling system, the combination of an inductance coil, atuning condenser having means for varying the capacity thereof, saidcoil and condenser being connected together to comprise a tuningcircuit, and adjusting means for said circuit whereby the maximumresonant frequency of the circuit and the rate of chan e of resonantfrequency of the circuit may e adjusted supplementally of said means forvarying the capacity of said condenser.

14. In a wave signaling system, the combination of an inductance coil, atuning condenser having means for varying the capacity thereof, saidcoil and condenser being connected together to comprise a tuningcircuit,

and adjusting means for said condenser,

whereby the maximum resonant frequency of said circuit and the rate ofchange of resonant frequency of said circuit may be adjustedindependently of said means for varying the capacity of said condenser.

15. In a radio-frequency signaling system wherein a plurality ofoscillatory circuits are simultaneously tunable over a certain resonantfrequency range by a unitary control, said frequency range havingmaximum and minimum limits, two separate means in each oscillatorycircuit other than said unitary control for determining, respectively,one point at or near the maximum limit of said frequency range andanother point at or near the minimum limit of said frequency range,

at which points all of said circuits may be individually adjusted bysaid means to-be in resonance with each other when tuned simultaneouslyby said unitary control.

16. In a multi-stage radio-frequency amplifier, the combination in eachstage of an inductance coil and a tuning condenser connected thereto,said condenser including capacity-varying means, each coil and condensertogether comprising an oscillatory circuit which is adjustably resonantover a certain frequency range by variation of the capacity of saidcondenser, and. a plurality of means other than said capacity-varyingmeans connected in each oscillatory circuit by which all of saidcircuits may be accurately adjusted individually to be in resonance witheach other at at least two different frequencies in said frequency rangewhen tuned simultaneously by said capacity varying means.

17 In a radio-frequency signaling system wherein a plurality ofoscillatory circuits are simultaneously tunable over a certain frequencyrange by a unitary control, two separate means in each oscillatorycircuit meother at at least said two different frequencies within saidfrequency range. 18. In a wavesignaling system wherein a plurality ofoscillatory circuits are intended to be simultaneously tunable over acertain frequency range by adjustment of a unitary control, the methodof bringing said oscillatory circuits into substantial resonance witheach other thruout said frequency range which comprises individuallyadjusting to resonance certain of said circuits at a frequency near onelimit of said range and then individually adjusting the same circuits toresonance at a frequency near the other limit thereof.

19. In a wave signaling system wherein a plurality of oscillatorycircuits are simultaneously tunable over a certain frequency denser ineach of said circuits for tuning the same by adjustment of the positionof said control, means connected in certain of said circuits forbringing all of said oscillatory circuits into resonance with each otherat a plurality of frequencies within said range, comprising oneadjustable electrical means for bringing-said circuits into resonance atone of the frequencies within said range when said unitary control is atacertain first position, and another adjustable electrical means forbringing said circuits into resonance at another frequency within saidrange when said unitary control is at a certain second position.

20..In a radio-frequency signaling system wherein a plurality ofoscillatory circuits are simultaneously tunable by a unitary control,

a variable condenser connected in one of said oscillatory circuits totune the same by variation of its electrostatic capacity, saidcondenserbeing characterized. in that it includes three adjusting means,the first of which operates in the usual manner to vary theelectrostatic capacity of said condenser between certain minimum andmaximum limits thereof, the second of which determines the said minimumlimit thereof, and the third of which determines the rate of change ofcapacity resulting from variation of the firstmentloned adjusting means.

21. In a multi-stage radio-frequency amplifier, a vacuum tube in eachstage having an input circuit and an output circuit, each input circuitincluding a coil and a variable condenser unit to tune said circuit tofrequencies within an intended operating freuency range, undesired couping between said stages whereby a tendency toward oscillation isproduced, means for limiting sa d tendency whereby detuning of any ofsaid stages for oscillation control 1s rendered unnecessary, a pluralityof ad usting means for at least one of said condenser units, each meansof said plurality having its predominant effect at a differentfrequency, whereby all of'isaid input circuits may be caused to havesubstantially identical electrical characteristics thruout saidoperating frequency range, and a single manual control mechanicallyinterconnecting said condenser units for tuning all of said inputcircuits simultaneously over said operating frequency range.

22. In a multi-stage radio-frequency amplifier, a vacuuin tube in eachstage having an input circuit and an output circuit, each input circuitincluding a coil and a variable condenser unit to tune said circuit tofrequencies within an intended operating frequency range, undesiredcoupling between the input and output circuits of certain of sa1d stageswhereby a tendency'towards oscillation is produced, means for limitingsaid tendency whereby detuning of any of said stages for oscillationcontrol is rendered unnecessary, a plurality of frequency-adjustin meansfor at least one of said input circuits, one of said frequency-adjustingmeans comprising a minimum-capacity adjustment for one of said condenserunits and another of said frequency-adjusting means comprising a searate adjustment for the rate of change 0 frequency of one of said inputcircuits, whereby all of said input circuits may be caused to havesubstantially identical electrical characteristics'thruout saidoperating frequency range, and a single manual control mechanicallyinterconnecting said condenser units for tuning all of said inputcircuits simultaneously over said operating frequency range.

23. In a multi-stage radio-frequency amplifier, a vacuum tube in eachstage having an input circuit and an output circuit, each input circuitincluding a coil and a variable condenser unit to tune said circuit tofrequencies within an intended operating frequency range, undesiredcoupling between the input and output circuits of at least one stagewhereby a tendency towards oscillation is produced, means for limitingsaid tendency whereby detuning of any of said stages for oscillationcontrol is rendered unnecessary, and a single manual control for tuningall of said input circuits simultaneously, certain of said condenserunits being provided with a plurality of substantially independentadusting means supplemental to said single manual control and soarranged with respect thereto that the capacity value of each of saidcertain condenser units may be separatelv and independently adjusted ata plurality of different frequencies, whereby all of said input circuitsmay be caused to have substantially identical electrical characteristicsthruout said operating frequency range.

24. In a radio-frequency amplifying system including a plurality ofvacuum tubes, each vacuum tube having an input circuit and an outputcircuit, at least one of said circuits of each tube being sharply tunedover an operating frequency range by means including a variablecondenser unit, undesired coupling between the input and output cirsuitsof at least one tube whereby a tendency towards oscillation is produced,means for limiting said tendency whereby detuning of any of saidcircuits for oscillation control is rendered unnecessary, and a singlemanual control for tuning simultaneously all of the circuits whichinclude said condenser units, certain of said condenser units beingprovided with a plurality of substantially independent adjusting meanssupplemental to said single manual control and so arranged with respectthereto that the capacity value of each of said certain condenser unitsmay be separately and independently adjusted at a plurality of differentfrequencies, whereby all of the circuits which include said condenserunits may be caused to have substantially identical electricalcharacteristics thruout said operating frequency range.

25. In a multi-stage radio-frequency amplifier, a Vacuum tube in eachstage having an input circuit and an output circuit, each input circuitincluding inductance and capacity, one of which is variable to tune saidcircuit to frequencies within an intended operating frequency range,undesired coupling between the input and out at circuits of certain ofsaid stages where y a tendency towards oscillation is produced, meansfor limiting said tendency whereby detuning of any of said circuits foroscillation control is ren- 4 dered unnecessary, a unitary controlcommon to said input circuits for simultaneously adjusting the resonantfrequency thereof within said operating frequency range, andsupplemental adjusting means connected in certain of said input circuitswhereby the maximum resonant frequency of each of said certain inputcircuits and the rate of change of resontant frequency of each of saidcertain input circuits may be individually adjusted so that all of saidinput circuits may have' substantially identical electricalcharacteristics thruout said operating frequency range.

26. In a radio-frequency signaling system wherein a plurality ofoscillatory circuits are simultaneously tunable over a certain frequencyrange by movement of a unitary control, adjust-ing means supplemental tosaid plurality of oscillatory circuits are simultaneously tunable. overa certain frequency range by the movement of a. unitary frequencycontrol, adjusting means connected in each of said oscillatory circuitsfor individually adjusting independently of the movement of saidfrequency control the rate of change of resonant frequency of each ofsaid circuits.

28. In a tuned radio-frequency amplifier having a plurality ofoscillatory circuits simultaneously tunable over a certain frequencyrange by the movement of a unitary control, adjusting means supplementalto said control for individually adjusting independently of the movementof said control the rate of change of resonant frequency of certain ofsaid circuits, whereby said oscillatory circuits may be maintainedsubstantially in resonance with each other when tuned over saidfrequency range by said unitary control.

29. In a radio-frequency signaling system wherein a plurality ofoscillatory circuits are simultaneously tunable over a certain frequency range by a unitary control, means supplemental to said controlfor adjusting the maximum resonant frequency and the rate of change ofresonant frequency of at least one of said circuits.

30. In a tuned radio-frequency amplifier having a plurality ofoscillatory circuits simultaneously tunable over a certain frequencyrange by a unitary control, means supplemental to said control forindividually adjusting the maximum resonant frequency and the rate ofchange of resonant frequency of certain of said circuits, whereby saidoscillatory circuits may be maintained substantially in resonance witheach other when tuned over said frequency range by said unitary control.

31. In a radio-frequency signaling system intended to have a pluralityof electrically similar oscillatory circuits, each said circuit beingintended to be tunable over the same frequency range by movement of afrequency control, a plurality of, substantially independent meansassociated with a certain one of said circuits and supplemental to saidfrequency control to adjust said certain circuit at as many differentfrequencies as there are means provided, so that adjustment of saidplurality of circuits from one of said different frequencies to anotherof said difi'erent frequencies requires the same extent of movement ofall of said frequency controls.

In testimony whereo I aflix m signature.

LOUIS A. HAZ LTINE.

LDISOLAIMEZR 1,755,114.Louis A. Hazeltine, Hoboken, N. J. UNICONTROLSIGNALING SYSTEM.

" Patent dated April 15, 1930. Disclaimer filed-January 18, 1936, by thepatentee, the assignee, Hazelt'ine Corporation, assenting.

Hereby enters this disclaimer to claims 10 29 of said patent.

[Oficial Gazette February 18, 1936.]

, 12, 13, 14, 16, 17, 19, 21.23, '24, and

